1. Field of the Invention
The present invention relates particularly to a production process suitable for obtaining a high quality vinyl chloride polymer having a low polymerization degree of an average polymerization degree being 850 or less.
2. Description of the Prior Art
A vinyl chloride polymer is generally produced by subjecting vinyl chloride monomer or a monomeric mixture containing vinyl chloride monomer to suspension polymerization in the presence of an oil-soluble polymerization initiator and a suspending agent in an aqueous medium.
Conventionally in order to improve the yield of the resulting polymer without extending the polymerization time, there have been known a method increasing the amount of an oil-soluble polymerization initiator to be used and a method elevating the temperature of a content present in a polymerization vessel when the polymerization reaction proceeds sufficiently and the internal pressure of the polymerization vessel begins to drop. However, the polymer obtained by such a method has the defect that the polymer becomes yellowish when it is formed into products; that is, the so-called initial discoloration of the formed products may increase. Thus, it is impossible that the conventional methods improves the yield of the resulting polymer as well as keeping the initial discoloration of the formed products at a low level.